The trends with automotive engine design are associated with increased operating temperatures and improved engine efficiency, which ultimately require higher quality lubricants. Automobile manufacturers and government regulators have introduced increasingly more stringent performance requirements for lubricants to comply with the ongoing environmental standards. As such, the specifications for finished lubricants are requiring products having excellent low temperature properties, high oxidation stability, low volatility and high viscosity indexes. Indeed, the increasingly demanding specifications require higher quality base oils that can be produced efficiently and economically.
In this aspect, Group II+ base oil, though not an official American Petroleum Institute (API) designation, is a term used to describe API Group II stocks of higher viscosity index (110-119) and lower volatility than comparable Group II stocks.
However, due to their high viscosity index and low volatility, API Group III base oils have become the base stocks of choice for the next generation of lubricant compositions. This in turn has resulted in greater demand for the supply of Group III base oils. Production of Group III base oils can be difficult and require the use of special high viscosity index gas oils, which can be higher in cost than the gas oils used to make Group II base oils. Additionally, the production of Group III base oils can involve severe hydrocracking of gas oils in order to obtain a viscosity index of at least 120. The severity of the hydrocracking conditions can shorten the life of the catalyst and negatively impact the yield by downgrading potential base oil to lower valued diesel and other light products.
An alternative can include co-feeding a high quality second feedstock with a lubricant oil feedstock directly to a hydrocracking unit in order to boost the viscosity index to Group II+ or Group III base oils. In this aspect, it would be advantageous if the second feedstock were low in cost and had additional benefits, such as a high viscosity index, low pour point and result in reduced environmental waste.
It has been discovered that ketones and beta-keto-esters may be formed from renewable fatty acid sources and then deoxygenated to afford high value base oils. Transforming renewable fatty acids into useful products presents a unique opportunity to address stringent performance requirements for lubricants. As such, there are numerous efforts underway to generate hydrocarbon base oils from renewable biomass. (e.g., Xiong et al., A Bio-Catalytic Approach to Aliphatic Ketones, Science Reports, 2, 311, pp. 1-7, Mar. 13, 2012). The preparation of ketones from carboxylic acids is well known and has been used in their preparation from carboxylic acids for many years. (e.g., Vogel's Textbook of Practical Organic Chemistry, Fourth edition, Longman N.Y. 1978, pp. 429-433). It is also well known that the reactions can be used to convert fatty acids such as stearic acid and other fatty acids of natural origin to ketones in the base oil boiling range. (e.g., U.S. patent application Ser. Nos. 13/486,097 and 13/157,921; and U.S. Pat. Nos. 7,850,841, 7,967,973 and 8,048,290). The preparation of beta-keto-esters from esters is well known and has been used in the preparation of beta-keto-esters from the commonly known Claisen condensation for many years. (e.g., March's Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, Fourth edition, Wiley-Interscience 1992, pp. 491-493).
In summary, the process disclosed herein provides several advantages over previously known techniques for producing Group II+ or Group III base oils. Adding the ketone or beta-keto-ester feedstock directly to the lubricant hydrocracker together with the traditional feedstock used for processing base oils gives a surprisingly large increase in the VI of the total base oil. The hydrocracking catalyst and process can handle higher oxygen levels in the feed, which is in contrast to the sensitivity of the hydroisomerization catalyst to oxygen and thus hydrotreating of the biologically derived feedstock prior to introduction to the lubricant producing hydrocracker will typically not be required. Furthermore, due to the linear carbon chains of the ketone or beta-keto-ester feedstock it may be less likely to crack to light products out of the base oil range.